1. Technical Field
This disclosure generally relates to an integrated circuit for determining eye patterns and an error rate associated with a communication channel. More specifically, this disclosure relates to an integrated circuit that includes an on-chip oscilloscope.
2. Related Art
Oscilloscopes are widely used to debug problems in communication channels. For example, an oscilloscope can be used to determine an eye pattern associated with a receiver on a link. However, an external oscilloscope is an expensive component that can alter the signal being measured because of the perturbation that occurs when a signal path is probed. This perturbation can make it difficult to diagnose problems in a communication channel.
In principle, an on-chip oscilloscope can address this challenge, thereby allowing accurate measurements of signals (including any distortion associated with the receiver package). For example, an analog-to-digital converter (ADC) can be implemented on-chip. However, in order to obtain sufficient resolution, an on-chip ADC typically includes multiple comparators, which are expensive, and which consume valuable area on an integrated circuit.
Alternatively, in some existing receivers a single comparator or slicer in a data path is used to implement an oscilloscope. While this approach does not consume additional area on the integrated circuit, it has several drawbacks. In particular, because the comparator outputs a ‘0’ or a ‘1’ based on a voltage offset and a timing signal (such as a clock signal), the voltage offset and the phase of the timing signal usually need to be swept over a range of values in order to measure an eye pattern (a two-dimensional graph of voltage as a function of time during a clock period that includes information about timing and voltage margins).
However, when sweeping the voltage offset and the phase of the timing signal, the normal function of the receiver is disrupted. Furthermore, the comparator or data slicer in on-chip oscilloscopes is typically located after an equalizer. Consequently, these on-chip oscilloscope designs make it difficult to diagnose and correct problems, which can increase the development time and expense.